docs: def ToInternal(self):
          """Convert to the internal representation of (angstroms, photlam).
          This is for internal use only.
  
          """
          self.validate_units()
  
          savewunits = self.waveunits
          savefunits = self.fluxunits
  
          if hasattr(self, 'primary_area'):
              area = self.primary_area
          else:
              area = None
  
          angwave = self.waveunits.Convert(self.GetWaveSet(), 'angstrom')
          phoflux = self.fluxunits.Convert(angwave, self._fluxtable, 'photlam',
                                           area=area)
  
          self._wavetable = angwave.copy()
          self._fluxtable = phoflux.copy()
  
          self.waveunits = savewunits
          self.fluxunits = savefunits